There are some pluses and minuses for both solutions…
Flair suffers less interferences with its proprietary protocol as Keen uses Zigbee… But at my home, Keen has been working fine (with the Keen Bridge has a repeater under ST) for more than 2 years (I haven’t changed the batteries yet with my DTH)…
I’ve had Flair for more than a year now and it’s working well so far… As it’s a cloud to cloud integration, it takes more time to set a level (0,50,100) due to servers load, network latency, etc… You cannot set a more precise level like Keen (ex. 25, 75,90)…
However, the Flair vents are usually less expensive than Keen.
Just my 2 cents…